The present invention relates to a press die for molding a sipe blade and a method for making the press die. More particularly, it relates to a press die for molding a sipe blade which can efficiently mold a sipe blade having a complicated shape such as three-dimensional shape and having excellent mechanical strength characteristics and which can reduce production cost due to its simple structure, and a method for simply and efficiently making a press die for molding a sipe blade having a complicated shape such as a three-dimensional shape by a casting method.
Tire molds are difficult to make by machining methods because they have complicated designs with sharp dent-shaped corner portions or undercut shapes, and generally they are made by casting methods. Of these molds, many of them are made of aluminum alloys, cast irons or cast steels. This tendency is conspicuous, especially, when the design shapes of tires have many grooves of about 0.1-3.0 mm in width which are called xe2x80x9csipesxe2x80x9d (specifically, studless tires, etc.) and these tire molds cannot be made by mechanical methods.
Here, the term xe2x80x9cmachining methodxe2x80x9d means forming methods other than those causing contraction in the molding, such as casting, and as examples thereof, mention may be made of various molding methods employed in conventional methods for making metal molds for molding two-dimensional shape sipe blades, such as wire electric discharge machining, NC machining which uses a ball end mill, and additionally, various methods which can directly mold the shape of metal molds, such as ultrasonic machining and electric discharge machining. Usually, wire electric discharge machining is employed because partial metal molds consisting of a pair of top and bottom molds can be obtained at a time. As for other molding methods, for example, partial metal molds consisting of a pair of top and bottom molds are obtained by making one of the molds and then making a reversal mold thereof.
As shown in FIG. 36, thick grooves 102 and 103 such as ribs and lugs are formed on a tire 101, but for special uses such as studless tires, sipes 104 which are thin grooves of about 0.1-3.0 mm in width are sometimes formed in addition to ribs and lugs to improve gripping force and drainage.
The sipes 104 are two-dimensional in shape, such as corrugated shape and zigzag shape at the ground contact face (profile face) for obtaining the effects of improving gripping force and drainage due to edge effects. Recently, for further improvement of tire performance, it is demanded that not only the profile face, but also the shape in the direction of diameter of tire have the similar two-dimensional shape (moreover, complicated curved faces such as a three-dimensional shape), namely, it is demanded to make the shape of sipes into three-dimensional shapes.
As shown in FIGS. 37(a)-37(e), since a three-dimensional shape sipe 107bcan improve block stiffness of tire 106 as compared with the conventional two-dimensional shape sipe 107a, the tire 106 does not undergo buckling even at driving and braking and can be further improved in gripping force.
When the shape of a tire mold having the above sipes is made by casting out, the mold strength is sometimes insufficient, and in this case, especially, when a tire mold made of an aluminum alloy is used, there is generally employed a method of casting-in a sipe blade previously made of a material of high strength. In this case, since a tire mold having sipe is complicated in its design, a casting method is used instead of machining method.
As shown in FIGS. 38(a)-38(e), according to conventional methods for producing a tire, it is generally produced by a method which comprises disposing a sipe blade 111 (hereinafter sometimes referred to merely as xe2x80x9cbladexe2x80x9d) at a pattern 112 for casting a tire mold(hereinafter sometimes referred to merely as xe2x80x9cpatternxe2x80x9d) and then casting with a molten metal a blade 114 having finally a shape complementary to sipe 104 (see FIG. 36) to integrate with a metal mold 116 for molding a tire which is a reversal mold. In FIGS. 38, a rubber mold 113 and a gypsum mold 115 are used.
As shown in FIGS. 39(a) and 39(b), as a result of pursuing both the cost and the productivity, the sipe blade 111 which is used for conventional method for producing a tire has been mainly produced by a method which comprises press molding a thin plate material 121 which is punched or laser cut (wire electric discharging cutting) using a press die 10a made by wire electric discharge machining.
However, as shown in FIGS. 39(a) and 39(b), since the press die 10a is made by wire electric discharge machining, this method can be adapted to only the press die 10a having a two-dimensional shape formed by linearly moving a wire 117, and the resulting sipe blade ill is limited to one which has a two-dimensional shape (having a corrugated shape in the monoaxial direction). Thus, it is difficult to obtain a sipe blade which can remarkably improve the tire performance. The sipe blade 111 shown in FIG. 39 (c) consists of a cross vent hole 122, a locking hole 123, a sipe formed portion 124, and a portion 125 which is cast in the metal mold for molding.
As a method for making a sipe blade having a three-dimensional shape, a method is known which comprises subjecting a press die for molding to three-dimensional NC machining by a ball end mill, and press molding a thin raw material using the press die, but this method is high in cost and is not practical.
Furthermore, there is proposed a method of making a press die for molding by a casting method (JP-A-62001-25831). However, according to this method, preparation of shape data or setting of complicated shape is sometimes difficult, and, for example, it has been very difficult to optionally combine a plurality of molded shapes as one protrusion unit of protrusive mountain shape (protrusive mountain shape or protrusive dimple shape).
Moreover, in many cases, a sipe blade of three-dimensional shape is required to be a combination of a plurality of those having basic shapes in which the number of the molded protrusive mountains is changed in the range of about 1-20 protrusive mountains. Therefore, according to conventional methods, metal mold or casting pattern must be made one by one, and this is troublesome.
For solving these problems, it is known that as shown in FIGS. 40(a) and 40(b), many divided press dies 131, 132 in which a minimum number of molded protrusive mountain shapes are divided are previously made (FIG. 40(a)), and these are combined in a desired shape to make one press die (combined (fabricated) mold). However, there is a problem that such combined (fabricated) press dies 133, 134, 135 are not suitable for mass-production from the point of strength or from the practical point.
As shown in FIGS. 41(a) and 41(b), when it is necessary that the sipe blade 141 has a basic shape (primary shape) consisting of protruded shapes (protrusive dimple) 144 and dented shapes (dented dimple) 145 (FIG. 41(a)), and additionally a molded shape (secondary shape) 143 which is larger than the basic shape in size is given to the whole sipe blade 141 (FIG. 41(b)), position of disposition of the primary shapes at the top and bottom molds of the divided press die must be changed, and it is very difficult to make a press die for molding with taking these points into consideration.
As shown in FIG. 42(a), there is a further problem that at the time of actual molding of sipe blades, in the case of the shape being more complicated, such as having the two-dimensional shape 153 and the three-dimensional shape 154, the drawn shape of the sipe blade after press molding has the curved shape 152, being different from the shape 151 assumed before press molding. Thus, it is difficult to put the peripheral shape in a given scope. This problem can be solved by trimming the peripheral shape of the sipe blade after press molding. However, it is more difficult to make a trimming die applicable to fine and complicated curved faces such as those of three-dimensional shapes than to make a press die. Thus, this method cannot be practically employed.
The curving phenomenon occurs for the following reasons. That is, when the total length shrinkage caused by molding is considered by minimum unit of molding, the reason is as follows.
As shown in FIG. 42(b), in the case of molding the material 155 of two-dimensional shape, the total length shrinkage 156 occurs uniformly in the whole area (strictly speaking, it appears that there is no change in extended length, and the length becomes shorter only in the chord length).
Further, as shown in FIG. 42(c), in the case of molding the material 157 of three-dimensional shape, the total length shrinkage 158 occurs non-uniformly. Therefore, the average total length shrinkage per one section becomes smaller than the case of two-dimensional molded shape which is the same in amplitude of molded protrusive shape (molded protrusive mountain or molded protrusive dimple). Therefore, when pitch and amplitude of the two-dimensional molded shape are set in correspondence to pitch and maximum amplitude of the three-dimensional molded shape such as protrusive dimple, the two-dimensional molded portion undergoes the greater total length shrinkage at the time of press molding to cause curved deformation as shown in FIG. 42(a).
The more complicated problem is that at the time of actual press molding, the phenomenon xe2x80x9csqueezingxe2x80x9d occurs due to the frictional resistance between the press die and the sipe blade material, resulting in total length elongation due to the reduction in thickness of the sipe blade.
Accordingly, there is the complexity of the problem in that even when the difference of the total length elongation can be analytically calculated from the molded shape, molding behavior corresponding thereto is not shown. In addition, there are all of the influences such as materials of sipe blades, materials of press die, surface state, lubrication condition, pressing conditions, and the like.
In order to solve these problems, there are proposed various methods for making sipe blades having a three-dimensional molded shape and methods for making press die thereof (e.g., JP-2000-280751 and JP-A-2001-91447). By employing these methods, the above problems can be solved and sipe blades of three-dimensional shape can be practically made, but as for the important three-dimensional shape per se of the sipe blades, those which satisfy all of remarkable improvement of tire performance, diminishment of generation of troubles in making tire molds and in maintenance thereof, and the like have not yet been proposed.
That is, the three-dimensional molded shape of the sipe blades used for conventional tire molds have the following problems.
As shown in FIG. 43(a) and FIG. 43(b), in the case of the sipe blade 111 of the three-dimensional molded shape as shown in xe2x80x9cpneumatic tirexe2x80x9d proposed in JP-A-2001-1722, the performance of the resulting tires have no problems, but as shown in FIG. 44(a) and FIG. 44(b), in the case of these sipe blades 111 being disposed in a tire mold 116 at a high density, when vent holes 161, etc. are to be opened in the mold per se from the side of curvature center of the mold, the sipe blade 111 which is disposed in the mold 116 and gives the corresponding sipe shape and a working tool interfere with each other (being obstructed by the dented and protruded shape of the sipe blade 111) to make it impossible to form the vent holes 161.
In the case of the shape of sipe blade disclosed in JP-A-20001-1722, it is difficult to draw the sipe blade out of the tire mold per se and re-plant it in repairing of the mold. In the technique of JP-A-2000-280751, the cast-in portion has no undercut shape, and thus the above trouble is overcome.
Similarly, as shown in FIG. 45, when xe2x80x9ccrank moldedxe2x80x9d shape in the xe2x80x9cpneumatic tirexe2x80x9d disclosed in JP-A-11-78432 is employed in three-dimensional molded shape, the troubles as mentioned above are apt to occur. In this case, the troubles caused by drawing and replanting of the sipe blade in repairing of mold do not occur.
Furthermore, as shown in FIG. 46, a great bending load sometimes acts on the tire mold, especially on the sipe blade at the time of molding of tire. In this case, whether the molded shape of the sipe blade can exhibit a great drag against the bending load or not affects the deformation and failure life of the sipe blade per se. This can be explained by a physical model corresponding to the bending of cantilever beam in material dynamics, and when the same material of sipe blade and plate thickness are used, the sipe blade having a molded shape which has a greater section modulus in respect to the axis of bending load can stand the greater bending load. Accordingly, by selecting a sectional shape greater in section modulus, a sipe blade stronger against the same bending moment can be obtained.
The section modulus here means a material dynamic parameter relating to the sectional shape of a beam as described, for example, in Seike Seiichiro""s Kogaku Kiso, xe2x80x9cZairyo Rikigaku (materials dynamics)xe2x80x9d published from Kyoritsu Shuppan Co.
As shown in FIG. 47(a) and FIG. 47(b), in the case of two sipe blades (planar sipe blade 111a and two-dimensional molded sipe blade 111b), both the sipe blades 111a and 111b produce a maximum bending stress at the section X against a bending load H. When they have the same thickness, the two-dimensional molded sipe blade 111b is greater in section modulus at the section X than the planar sipe blade 111a, and, hence, the two-dimensional molded sipe blade 111b is smaller in the maximum bending stress generated at the section X.
As shown in FIG. 48(a) and FIG. 48(b), in the case of a dimpled three-dimensional molded shape, the sectional shape becomes nearly planar at the portions {circle around (1)}and {circle around (2)}against the bending load, and these portions become smaller in section modulus than other portions. Therefore, when a bending load acts on the three-dimensional molded sipe blade 111c, troubles such as deformation and breakage are apt to occur at the portion {circle around (1)}on which a larger stress acts and thus there occurs a problem in strength.
As shown in FIG. 49(a) and FIG. 49(b), in the case of the three-dimensional sipe blade 111c disclosed in JP-A-2001-1722, the similar phenomenon also occurs, and section modulus of the portion shown by a one-point chain line becomes smallest and, as a result, deformation or breakage is apt to occur at this portion. This sipe blade 111c gives satisfactory performance of the resulting tire, but the strength characteristics as a tire mold is not sufficient.
The present invention has been made in view of the above problems. The object of the present invention is to provide a press die for molding a sipe blade by which a sipe blade having a complicated shape such as a three-dimensional shape and having excellent mechanical strength characteristics can be efficiently molded and which has a simple structure and can reduce the production cost, and a method for making simply and efficiently a press die for molding a sipe blade having a complicated shape such as three-dimensional shape by a casting method.
As a result of intensive research conducted by the inventors for attaining the above objects, it has been found that the above object can be attained by the following procedures. That is, basically, as a pattern used for the method for making a press die for molding a sipe blade utilizing a casting method, a metal mold having a shape which is reverse to the shape of the press die for molding sipe blade is made by machining or the like, and a portion of the press die for molding a sipe blade to which a load is applied by molding pressure in contact with a material for the sipe blade is allowed to have a shape (normal shape) corresponding to the desired shape of the sipe blade in order to impart the desired shape to the sipe blade, and, besides, a portion to which a load is not applied by the molding pressure without contacting with the material for the sipe blade is allowed to have a relief part which does not correspond to the desired shape of the sipe blade and dose not substantially contact with the sipe blade after molded. Thus, the present invention has been accomplished. That is, the following press die for molding a sipe blade and a method for making the mold are provided by the present invention.
According to a first aspect of the present invention, a press die for molding a sipe blade which comprises a pair of divided parts composing a press die between which a material of the sipe blade is interposed and pressed to mold a sipe blade having a desired shape, characterized in that a portion of each of the pair of the divided parts composing a press die to which a load is applied by a molding pressure in contact with the material for the sipe blade has a shape corresponding to the desired shape of the sipe blade in order to impart the desired shape to the sipe blade, and the portion to which a load is not applied by the molding pressure without contacting with the material for the sipe blade has a relief part which dose not substantially contact with the sipe blade after molded.
According to a second aspect of the present invention, a press die for molding a sipe blade according to the first aspect is provided, wherein the pair of the divided parts composing a press die are made using a machining method or a casting method.
According to a third aspect of the present invention, a press die for molding a sipe blade according to the first or second aspects is provided, wherein a first relief part which does not substantially contact with the sipe blade has a depth equal to or greater than the height of the opposing portions to which a load is applied by the molding pressure and comprises a groove having a bottom horizontal to the surface of the material of the sipe blade.
According to a fourth aspect of the present invention, a press die for molding a sipe blade according to any one of the first to third aspects is provided, wherein the pair of the divided parts composing a press die have three-dimensional dented and protruded shape corresponding to the shape of the sipe blade, the portion of the metal molds to which a load is applied by the molding pressure due to contact with the material of the sipe blade has a protruded shape, and the portion to which a load is not applied by the molding pressure without contacting with the material for the sipe blade has a dented shape.
According to a fifth aspect of the present invention, a press die for molding a sipe blade according to the fourth aspect is provided, wherein the shapes of the pair of the divided parts composing a press die are discontinuous with individually and independently maintaining the plurality of the three-dimensional shapes, and a second relief portion which does not substantially contact with the material for sipe blade is formed at the crossing part thereof.
According to a sixth aspect of the present invention, a press die for molding a sipe blade according to the fourth aspect is provided, wherein in correspondence to the shape of the sipe blade, the shapes of a pair of divided parts composing a press die are three-dimensional dented and protruded shapes having a primary molded shape and a secondary molded shape and have a plurality of protruded shape portions to which a load is applied by the molding pressure in contact with the material for sipe blade and are disposed so that a curved face formed by connecting the apexes of the protruded shape portions forms a primary molded shape.
According to a seventh aspect of the present invention, a method for making a press die for molding a sipe blade is provided, comprising a pair of divided parts composing a press die between which a material of the sipe blade is interposed and pressed to mold a sipe blade having a desired shape by forming a pattern having a shape reverse to the shape of the pair of the divided parts composing a press die and then forming from the pattern a casting having a shape reverse to that of the pattern, characterized in that a plurality of patterns having a shape reverse to the shape of the pair of the divided parts composing a press die are formed so that the pair of the metal molds have such shape that the portion to which a load is applied by molding pressure in contact with the material for the sipe blade has a shape corresponding to the desired shape of the sipe blade and the portion to which a load is not applied by molding pressure without contacting with the material for the sipe blade is provided with a first relief part which does not correspond to the desired shape of the sipe blade and does not substantially contact with the sipe blade after molded, and then a casting having a shape reverse to the pattern is formed.
According to an eight aspect of the present invention, a method for making a press die for molding a sipe blade according to the seventh aspect is provided, wherein a plurality of the patterns having a shape reverse to the shape of the pair of the divided parts composing a press die are formed by a machining method and then the castings having the shape reverse to the patterns are formed by a casting method.
According to a ninth aspect of the present invention, a method for making a press die for molding a sipe blade according to the seventh or eighth aspects is provided, wherein the first relief part which does not substantially contact with the sipe blade comprises a groove having a depth equal to or greater than the height of the protruded shape of the opposing divided parts composing a press die and, besides, having a bottom horizontal to the surface of the material for the sipe blade.
According to a tenth aspect of the present invention, a method for making a press die for molding a sipe blade according to any of the seventh to ninth aspects is provided, wherein the shape of the portions to which a load is applied by the molding pressure in contact with the material for the sipe blade is allowed to have a protruded shape and the shape of the portions to which a load is not applied by the molding pressure without contacting with the material for the sipe blade is allowed to have dented shape so as to give a three-dimensional dented and protruded shape to a pair of divided parts composing a press die in correspondence to the shape of the sipe blade.
According to an eleventh aspect of the present invention, a method for making a press die for molding a sipe blade according to the tenth aspect is provided, wherein a plurality of protruded portions to which a load is applied by the molding pressure in contact with the material for the sipe blade are formed and simultaneously apexes of the protruded portions are disposed so that a curved face formed by connecting the apexes forms the primary molded shape so as to give a three-dimensional dented and protruded shape to the pair of divided parts composing a press die in correspondence to the shape of the sipe blade.
According to a twelfth aspect of the present invention, a method for making a press die for molding a sipe blade according to any of the seventh to eleventh aspects is provided, wherein a plurality of pattern parts divided into basic shapes commonly included in the plurality of the shapes of the sipe blade are previously prepared and these pattern parts are optionally combined to construct the pattern so that sipe blades having a plurality of shapes can be optionally provided.
According to a thirteenth aspect of the present invention, a method for making a press die for molding a sipe blade according to any one of the seventh to eleventh aspects is provided, wherein the pattern is formed so that the shapes of a pair of divided parts composing a press die are discontinuous with individually and independently maintaining a plurality of the shapes, and a second relief part which does not substantially contact with the material for sipe blade is formed at the crossing part.
According to a fourteenth aspect of the present invention, a method for making a press die for molding a sipe blade according to any one of the seventh to thirteenth aspects is provided, wherein a first reversal mold having a first shape reverse to the shape of the pattern or combination thereof (reversal mold, etc.) is formed, a first sipe blade replica comprising a material easy in molding, such as sheet wax, is molded using the resulting reversal mold using the resulting reversal mold, a second shape is imparted to this first sipe blade replica using a given molding mold to mold a second sipe blade replica having both the first shape and the second shape, a pair of second reversal molds having a shape reverse to the shape of the second sipe blade replica is formed using the second sipe blade replica, and a casting having both the first shape and the second shape is formed from the second reversal mold using a casting method.
According to a fifteenth aspect of the present invention, a method for making a press die for molding a sipe blade having less protruded shapes than the dented shapes of the pattern and/or the second reversal mold obtained in the intermediate stage in the method according to any one of the seventh to fourteenth aspects using the pattern or the second reversal mold obtained in the intermediate stage in the method according to any one of the seventh to fourteenth aspects, or combination thereof (pattern, etc.) is provided, characterized in that the dented shape portion of the pattern and/or the second reversal mold is filled with a filler so that the surface of the dented shape portion is in one plane, thereby forming a new pattern, and a casting having a shape reverse to the shape of this new pattern is formed from the new pattern by a casting method.
According to a sixteenth aspect of the present invention, a method for making a metal mold for trimming a sipe blade (trimming die) having a given shape from a sipe blade rough mold which is larger in size than the sipe blade and formed by molding a material for the sipe blade is provided, characterized in that a third sipe blade replica larger than the sipe blade and comprising a material easy in molding such as sheet wax is molded from the pattern, the first reversal mold having the shape reverse to the shape of the new pattern or the mold for the secondary molded shape formed in the intermediate stage of the method according to any one of the seventh to fifteenth aspects, or combination thereof (reversal mold, etc.), a pair of third reversal molds are made using the third sipe blade replica, and a trimming die is formed using the third reversal mold by a casting method.
According to a seventeenth aspect of the present invention, a method for making a press die for molding a sipe blade is provided, comprising a pair of divided parts composing a press die between which a material of the sipe blade is interposed and pressed to mold a sipe blade having a desired shape by forming a pattern having a shape reverse to the shape of the pair of the divided parts composing a press die and then forming a casting having a shape reverse to the shape of the pattern, characterized in that the portion of the pattern corresponding to the dented and protruded shape in the secondary molded shape of the pair of the divided parts composing a press die is formed by using a cutter mark in a chemical molding method, a physical corrosion method or a machining method so that the pair of the metal molds have a three-dimensional dented and protruded shape having a primary molded shape and a secondary molded shape provided with a dented and protruded shape.
According to an eighteenth aspect of the present invention, a method for making a press die for molding a sipe blade according to the seventeenth aspect is provided, wherein a chemical etching method is employed as the chemical molding method.
According to a nineteenth aspect of the present invention, a method for making a press die for molding a sipe blade is provided comprising a pair of divided parts composing a press die between which a material of the sipe blade is interposed and pressed to mold a sipe blade having a desired shape by forming a pattern having a shape reverse to the shape of the pair of the divided parts composing a press die and then forming a casting having a shape reverse to the shape of the pattern, characterized in that the portion of the pattern corresponding to the dented and protruded shape in the secondary molded shape of the pair of the divided parts composing a press die is formed by using a porous material as a material of the pattern so that the pair of the metal molds have a three-dimensional dented and protruded shape having a primary molded shape and a secondary molded shape provided with a dented and protruded shape.
According to a twentieth aspect of the present invention, a sipe blade for a tire mold is provided, which is molded using a press die for molding a sipe blade according to any one of the first to sixth aspects.
According to a twenty-first aspect of the present invention, a sipe blade for a tire mold is provided, which is molded using a press die for molding a sipe blade made by a method for making a press die for molding a sipe blade according to any one of the seventh to fifteenth and seventeenth to nineteenth aspects.
According to a twenty-second aspect of the present invention, a sipe blade for a tire mold according to the twentieth or twenty-first aspects is provided, which has a xc2xd pitch of 1-5 mm and an amplitude of 1-5 mm of the primary molded shape and a xc2xd pitch of 0.05-2.5 mm and an amplitude of 0.05-2.5 mm of the secondary molded shape.
According to a twenty-third aspect of the present invention, a tire mold formed by using the sipe blade for a tire mold is provided according to any one of the twentieth to twenty-second aspects.